Effect of Electrolyte Composition and Concentration on Pulsed Potential Electrochemical CO2 Reduction

With rising CO2 emissions and growing interests towards CO2 valorization, electrochemical CO2 reduction (eCO(2)R) has emerged as a promising prospect for carbon recycling and chemical energy storage. Yet, product selectivity and electrocatalyst longevity persist as obstacles to the broad implementation of eCO(2)R. A possible solution to ameliorate this challenge is to pulse the applied potential. However, it is currently unclear whether and how the trends and lessons obtained from the more conventional constant potential eCO(2)R translate to pulsed potential eCO(2)R. In this work, we report that the relationship between electrolyte concentration/composition and product distribution for pulsed potential eCO(2)R is different from constant potential eCO(2)R. In the case of constant potential eCO(2)R, increasing KHCO3 concentration favors the formation of H-2 and CH4. In contrast, for pulsed potential eCO(2)R, H-2 formation is suppressed due to the periodic desorption of surface protons, while CH4 is still favored. In the case of KCl, increasing the concentration during constant potential eCO(2)R does not affect product distribution, mainly producing H-2 and CO. However, increasing KCl concentration during pulsed potential eCO(2)R persistently suppresses H-2 formation and greatly favors C-2 products, reaching 71 % Faradaic efficiency. Collectively, these results provide new mechanistic insights into the pulsed eCO(2)R mechanism within the context of proton-donator ability and ionic conductivity.